Recently, in the application of non-aqueous electrolyte secondary batteries to a small portable device such as mobile telephones or laptop computers, the capacity per unit volume is important, and therefore graphitic materials with primarily large density have been used as anode active materials.
On the other hand, the notion of mounting large lithium-ion secondary batteries, having high energy density and excellent output characteristics, in electric vehicles has been investigated in response to increasing concern over environmental issues. However, lithium-ion secondary batteries for vehicles are large and expensive, and are thus difficult to replace.Therefore, the lithium-ion secondary batteries for vehicles are required to have at least the same durability as that of the vehicles and demanded to have a product life of 10 years or longer (high durability).
Not only are high-performance lithium-ion secondary batteries used as power sources in small portable devices and next-generation vehicles such as electric and hybrid vehicles, they are also used in energy storage for power peak shifting and renewable energy stabilization.
That is, lithium-ion secondary batteries are used in a variety of applications, and therefore the required performance of a lithium-ion secondary battery differs greatly depending on application.
When applications are classified according to the scale of lithium-ion secondary battery, four typical applications are considered: “system,” “industrial,” “medium-scale grid,” and “residential.”
“System” applications include cases where lithium-ion secondary batteries are installed in a large-scale solar photovoltaic power plant (so-called megasolar), a wind power station, or the like, and cases where they are installed in a substation or the like. In “industrial” applications, lithium-ion secondary batteries are installed in factories, commercial facilities, large-scale housing complexes, or the like, or are used for excess power storage of renewable energy or storage for power peak shifting.In “medium-scale grid” applications, lithium-ion secondary batteries are installed in schools, urban areas, buildings, or housing complexes.In “residential” applications, small storage batteries are installed in individual residences.In such lithium-ion secondary battery applications, further cost reduction, extension of lifetime, increased energy density, and the like are required.
The following manufacturing method has been widely used for producing anodes of conventional general lithium-ion secondary batteries.
A binder is added to an anode active material and dissolved with an organic solvent or water.
Additives such as a conductive agent are added as necessary, and the obtained mixture is kneaded to form a slurry.
One or both faces of a metal foil current collector made from copper, nickel, or the like is coated with this slurry by a method such as doctor blading.
This is dried, and then made into an electrode by pressing.
Then, the obtained electrode is cut to a prescribed width and length, and laminated together with a cathode and a separator, and then an electrolyte is added, to produce a lithium-ion secondary battery.
As described above, lithium-ion secondary batteries are used not only as power supplies of small portable devices but in vehicular applications as well. Additionally, large lithium-ion secondary batteries are also widely used in load leveling applications through power storage.
In the field of small portable devices, the demand for high capacity, high durability, and reduced manufacturing cost gets stronger as devices increase in functionality.
On the other hand, in the field of large-scale batteries, the demand for high durability, high reliability, and reduced manufacturing cost is strong.
To satisfy such requirements for lithium-ion secondary batteries, high charge/discharge capacity, high coulombic efficiency, high durability, reduced electrode resistance, and reduced cost are anticipated in anode materials.
Manufacturing an anode in a lithium-ion secondary battery, as described above, includes an active material slurry production step, a step of coating a current collector, a drying step, and a compression molding step.
That is, it requires expensive manufacturing equipment and complex processes. Additionally, the uniformity of electrode coating greatly affects variations in battery performance.
Furthermore, the speed of the coating step and drying step greatly affects battery manufacturing capacity.
Therefore, if the electrode production process in the battery manufacturing process could be simplified, not only would quality stability and battery productivity be improved, but reduced battery manufacturing cost could also be expected.